Manufacture of leather using a modified vinyl ether-maleic anhydride copolymer, and resulting product



Unite MANUFACTURE 3F LEATHER USKNG A MBDH FED VTNYL ETHER-MALEHCANHYDRIDE C33- PULYlt ER, AND REULTENG PRUDUCE Joseph S. Kirk, Newtown,Pa, assignor to Generai 85 Film Corporation, a corporation of DeiawareNo Drawing. Application December 255, N51, Serial No. 263,985

12 Claims. (Si. 8-94.33)

the ammonium salt-half amide, the converted copolymers employed in suchtreatment and the products produced thereby.

There is a demand on the part of tanners of lightweight skins such ascalfskins and goatskins for a product or a method which will permit theuse of chromium salts as tanning agents but which will avoid the emptyunfilled character of chrome tannage and yet not detract from the clearneutral color of chrome leather and its normal afiinity for acidic typedyestuffs. It is recognized by the tanning art that salts of chromiumhave many virtues which are desired both by the tanners and the users ofleather. Chief among these are the high degree of stability of theleather, the simplicity of the tanning operation and high degree ofsubstantivity to all acidic type dyestuffs. Chrome leather has thedisadvantage, however, in being empty and unfilled, lacking theroundness and body which is generally desired of leather. This is ofparticular disadvantage to tanners of lightweight skins.

Vegetable-tanned leather, or the leather produced by subjecting skins tothe action of the natural plant tanning extracts, has most of theattributes of fullness and body required of leather. It lacks theextreme resistance to deterioration of chrome tanned leather, and inaddition is frequently dark colored and has generally poor afiinity forthe direct or cotton type dyestuffs. In addition, vegetable-tannedleather is less resistant to reversal by alkalis and hot water than ischrome tanned leather. For these reasons special precautions must beobserved in the manufacture of leather by vegetabletanning processes.

In order to improve the body and fullness of chrome tanned leather manymaterials have been tried. Among these are the sulfonated aromaticcondensates, various organic acids (masking agents) and other agents.The sulfonated aromatic condensates as a rule are sensitive to light,becoming discolored upon exposure to light, and in addition have astrong retarding action on the absorption of acidic dyestuifs, causingweak and washed out shades. The organic acids such as formic, acetic andphthalic acids etc. have a modifying action on the deposition of thechrome in the skin but do not materially contribute to the filling andbodying action. They have no pronounced effect on the dyeingcharacteristics of the leather.

it is an object of this invention to provide a method for fulling,Plumping, stuffing and improving the dye receptivity and otherproperties of hides, skins and leather before, during or after tanning.Another object of this invention is the provision of a compositionuseful in the aforementioned method. A further object is the provisionof improved hides, skins and leather. Other objects will appear as thedescription proceeds.

States Patent These objects are attained by the instant invention whichcomprises treatment of hides, skins and leather with a vinylether-maleic anhydride copolymer in which from about 5 to 15% of theanhydride groups have been converted to the salt-half amide with amember of the group consisting of ammonia and lower aliphatic primaryand secondary amines. The use of the aforementioned converted copolymersresult in the following unique properties and advantages which are ofgreat value to the leather trade:

When used in conjunction with chrome tannage they impart body andfullness to the leather. They may be applied either prior to chrometanning, during, or subsequent to it. When applied to hides, skins andleather as above they cause no appreciable alteration in theirreceptivity to dyestuffs, in contrast to previously employed expedients.Full uniform shades and blacks are easily obtained on susequent dyeingoperations. They are insensitive to any concentration of salt or acidused in tanning and they are not precipitated from solution by 10% saltor 2% sulfuric acid. They may accordingly be used on bated stock priorto pickling and the salt and acid added to the skins as in normalpickling operations. They require no special alteration of procedurefrom customary methods of chrome tanning. They may be applied to pickledskins at pH 2.5-4.0, and after absorption by the skin, chorme tanningsolutions may be applied directly to it. They are only mildly astringentand do not cause case hardening of the surface of the leather. Their usehas been found to improve the body, feel and fullness of suede leatherproducing a fine uniform nap to the suede. This latter characteristic isof extreme importance to suede manufacturers.

The converted copolymers of the instant invention may be produced in amanner well known in the art. Suitable methods for producing the initialcopolymer by condensation between the maleic anhydride and the vinylether are described in U. 3. Patent No. 2,047,398 and others. Theproduction of the full ammonium salt (substantially complete conversionof anhydride groups) of a vinyl ether-maleic anhydride half amidecopolymer is disclosed in U. S. Patent No. 2,313,565, but it isemphasized that no claim is made to the methods and compositionsdescribed therein since it has been found that copolymers in which morethan about 15% of the anhydride groups have been converted to thesalt-half amide with a member of the group consisting of ammonia andlower aliphatic primary and secondary amines are undesirable for thetreatment of hides, skins and leather in accordance with the instantinvention. They are taken up much more slowly by the hides, skins andleather, and produce decreased plumping, fulling and stufiing effects.On the other hand, at least about 5% of the anhydride groups should beconverted to the salt-half amide since otherwise the solubility inaqueous media, speed of take-up, and plumping, fulling and stuflingeifects are insufiicient. Within the range of about 5 to 15% conversionthe copolymers of the invention have been found to possess, as comparedfor example with the unconverted or initial copolymers, the highlydesirable properties of increased solubility in aqueous media, fastertake-up by the hides, skins and leather, increased plumping, stufiing,fulling and bodying action, and the like. The preferred range is from 8to 12% conversion, and within this range a copolymer with about an 11%conversion has been found to give optimum results.

While the preferred copolymer for use in the instant invention is thevinyl methyl ether-maleic anhydride copolymer, other vinyl ether-maleicanhydride copolymers may be used which are sufficiently water solubleand resistant to the action of salts and acids, as for example, thosederived from n-butyl, isobutyl, Z-methoxyethyl (from vinylation ofmethyl Cellos-olve), 2- ethoxyethyl (from vinylation of Cellosolve) andespecially vinyl ethyl ethers. Dry ammonia is preferred for conversionof the requisite number of anyhydride groups in the copolyrner toammonium salt, half amide groups, but other amines may be employed whichproduce converted copolymers with the desired solubility,non-sensitivity and other properties. Such other amines are for the mostpart in the lower aliphatic group, such as dimethyl amine, ethanolamineand the like. It will be understood that use of amines other thanammonia for the conversion will result in production of thecorresponding amine salts of the corresponding half-substituted amidesof the initial vinyl ether-maleic anhydride copolymers.

The converted copolymers of the invention possess the additionaladvantageous properties of dissolving in aqueous media to produce a pHwithin the operative range for producing the desired results, which isfrom about 2.5 to 4.0. Accordingly, unless influenced by other factors,no pH adjustment of the resulting solution with its attendantdisadvantages is necessary. Thus, for example, by merely dissolving acopolymer with about an 11% anhydride conversion in water a solution isobtained with a pH of about 3.8, whereby no adjustment of pH by additionof acids or bases need be made before treatment of hides, skins andleather therewith. The preferred pH range is from 3.0 to 3.8.

In general, the converted copolymers of the invention may beincorporated in amounts of about 0.5 to 6% based on the weight of thehides, skins or leather, Impregnation is generally accomplished fromaqueous media at any suitable temperature and for a period of time sufficient to allow impregnation in the desired amount. Since the processproceeds by way of exhaustion, the amount incorporated into the hides,skins and leather will depend essentially on the total amount ofconverted copolymer in the treating bath and the duration of treatment,and not on the concentration of the treating bath. The concentration ofthe treating bath may accordingly range from the saturation point downto that suflicient to supply the total amount of copolymer desired to beincorporated. The temperature, duration, concentration, and otherconditions of treatment will of course be some what dependent on thecharacter of the skin or leather being treated and the results desired.In general, operating temperatures on raw skins are usually held belowabout 85 F. On chrome leather, after-treatment temperatures as high as140 F. may be used. Too large an amount of copolymer, when applied toblue chromed skins, is diflicult to exhaust from solution and gives toomuch fullness, yielding a bloated, over-plump character to the skin.Likewise, too large an amount when used on drained, pickled skins,although readily exhausted, imparts more than the desired plumpness tothe leather with resultant loss of footage. Obviously, the lowestamounts effective for producing the desired results are economicallydesirable. The aqueous medium containing the converted copolymers of theinvention may also contain other common leather and skin treatingadditives, buffering agents and the like, which do not detract from thedesired result.

While the copolymers of the invention may be employed in conjunctionwith any tanning agents such as alum, natural tanning agents and thelike, it is especially advantageous in the production of chromedleather. In such production the converted copolymer may be used eitherprior to tanning with chrome or may be applied on the shaved blue stock.Excellent filling and plumping have been obtained by either method. Theuse on blue shaved stock permits selection for weight at the end of thetannage and is definitely advantageous in building up light-weightstock. Use after tanning has the further advantage of not requiring anychanges in the complex tanning formulations and procedures already beingem ployed by the tanners. However, since at a pH of about 3.0 to 3.3chrome solutions cause a rapid rise in the viscosity of solutions of theconverted copolymers employed in this invention, with resultant decreasein the amount and speed of take-up by the skins and leather, care shouldbe taken in applying such solutions to chromed, tanned to avoid thepresence of appreciable quantities of uncombined or unneutralizedchrome. This may be accomplished by washing.

The hides, skins and leather which may be treated in accordance with theinstant invention may be from any of the common sources. The leatherproduced is plumped, fulled, bodied, stuifed, and has a soft and mellowfeel. Because of the mild, non-astringent character of the treatment itmay be used in the production of grain leathers in order to increase thebody. In the production of suede kid the leather has a more uniform napwith much better bufiing qualities than obtainable by other plumpingagents or chrome alone. The color is not reduced as with other products,thus yielding full bloomy blacks on subsequent. dyeing. In most casesthe color is definitely superior to straight chromed leather.Lightweight goatskins are definitely plumped. Calf suedes and splits arelikewise improved. Of course in the treatment of any of the hides, skinsand leather their pH should be taken into consideration in order thatoptimum results may be obtained. Slight adjustment of the pH of thetreating solution may be necessary to compensate therefor. The leatherproduced in accordance with this invention may be subjected to any ofthe various kinds of finishing treatments customarily used.

The following examples are illustrative of the instant invention and arenot to be regarded as limitative:

Example 1 1330 grams of vinyl methyl ether-maleic anhydride copolymer(NsP250.76) were suspended in 6500 cc. of benzene. 35 grams of anhydrousammonia were bubbled through the slurry over a period of 4 hours at50-55 C. After all the ammonia had been added, the slurry was warmed for30 minutes, filtered and the filtrate washed with benzene and dried invacuum to yield 1355 grams of dry powder. Nitrogen analysis indicatedthat about 11% of the initial anhydride groups in the copolymer had beenconverted to the ammonium salt of its half amide.

Example 2 375 grams of chrome tanned calf leather were thoroughly washedfor 15 minutes, drained, and then immersed in 2000 cc. of water. Theproduct of Example 1 was easily dissolved in warm water in an amount toproduce a 10% aqueous solution, of which 112 cc. were added to theleather treating bath. The addition amounted to about 3 of the saidproduct on the weight of the leather. After 15 minutes of working, thebath had a pH of 3.1. The leather was worked in the bath for 40 moreminutes, after which 11.2 grams of Tanolin R (commercial chromiumsulfate containing 25% CrzOz) were added. The leather was then worked inthe bath for one hour longer, at which time the measured pH of the bathwas 3.0. 4 grams sodium bicarbonate were added to the bath and theleather worked therein for an hour longer, removed, washed and horsedup. The treated leather had a highly desirable plumpness and fullness offeel, somewhat like a vegetable-tanned product, and was readily dyed toany shade. The converted copolymer was taken up by the leather from thebath in a comparatively rapid and complete manner.

Example 3 1000 grams of Nigerian skins, drained pickle weight, wereworked for 15 minutes in a bath containing 20 grams of salt and 7.5grams of anhydrous sodium acetate in 1000 cc. of water. There was thenadded a solution of 30 grams of the product of Example 1 (3% on theweight of the skin) in 400 cc. of water. Said solution was previouslymade by dissolving the said product in hot water and had a pH of 3.8without any adjustment with alkali being necessary. After running for 1%hours, the pH was measured at 3.5 and 50 grams of iron free aluminumsulfate were added to the bath. After running for another 5 minutes, 7.5grams of soda ash were added. After working the skins in the bath for 30minutes longer, there was added a solution of 100 grams of Tanolin R(commercial chromium sulfate containing 25% CrzOs) in 500 cc. of water.The skins were worked in the bath for 1%. hours longer, the pH measuredat 3.2, and 15 grams sodium bicarbonate added. After working for 30minutes longer, the pH was 3.6 and grams of sodium bicarbonate added.The skins were worked in the bath for 30 minutes, at which time the pHwas 3.95. The skins were then removed, washed and horscd up. The treatedskins were plump and solid, and were readily dyed in light or darkshades. The converted copolymer was taken up by the skins from the bathcomparatively rapidly and completely.

Example 4 The process of Example 3 was repeated except that an 11%converted vinyl ethyl ether-maleic anhydride copolymer was employed.Improvements similar to those obtained in Example 3 were obtained.

Example 5 Skins treated in accordance with Example 3, were pearled,crusted and bufled in accordance with the normal practice of the art.They were wet back with 1% ammonia (28%) and /2% wetting agent in 7times their weight of water at 135 F. The skins thus prepared for dyeingwere divided into two parts.

One part of the skins were dyed in known manner in the regular developedblack process using:

18% Diazo Black BHN conc. (C. I. 401) 3% sodium nitrite 4% metatoluylenediamine After coloring the skins were fatliquored, crusted, staked,buffed and dry milled in the customary suede procedure. The finishedskins were then compared with regular chrome suede leather dyed andtreated by identical procedure and were found to have a shorter silkiernap and a fuller bloomier color.

Example 6 The other part of the skins prepared for dyeing in theprevious example were, in known manner, colored black by dyeing in adrum at 140 F. with 18% of a dyestuft mixture composed as follows:

40% Chrome Leather Fast Black 86 conc., Pr 371 Sulphon Cyanine 5RA Extraconc., C. I. 284 15% Resorcine Brown G, C. I. 234

20% Benzo Dark Green BA-CF, C. I. 583

10% Ethyl Acid Violet 4B conc., C. I. 53

The dyestuif was applied in two additions using 10% and 8% respectivelyfollowed by two additions of formic acid of 3% each. The skins wereprocessed after coloring as in Example 5. The finished skins were foundto be of excellent suede having a deeper bloomier color than regularchrome leather dyed in a similar manner.

Example 7 The product of Example 4 was prepared and colored by theprocedure of Example 5, producing an improved colored leather ascompared with leather which had not been treated with the convertedcopolymer.

Various modifications and variations of this invention will be obviousto a worker skilled in the art and it is understood that suchmodifications and variations are to be included within the purview ofthis application and the spirit and scope of the appended claims.

Unless otherwise indicated, the proportions recited above are based onthe weight of the hides, skins and leather being treated.

What is claimed is:

1. A process comprising treating hides, skins and leather with a loweralkyl vinyl ether-maleic anhydride copolymer in which at least about 5and no more than 15 of the anhydride groups have been converted to thesalt-half amide with a member of the group consisting of ammonia andlower aliphatic primary and secondary amines.

2. The process of claim 1, in which the vinyl ether is vinyl methylether.

3. The process of claim 2, in which about 11% of the anhydride groupshave been converted to the ammonium salt-half amide.

4. The process of claim 1, in which the vinyl ether is vinyl ethylether.

5. The process of claim 4, in which about 11% of the anhydride groupshave been converted to the ammonium salt-half amide.

6. A process comprising treating hides, skins and leather in an aqueousmedium with a lower alkyl vinyl ether-maleic anhydride copolymer inwhich at least about 5 and no more than 15 of the anhydride groups havebeen converted to the salt-half amide with a member of the groupconsisting of ammonia and lower aliphatic primary and secondary amines.

7. A process comprising treating hides, skins and leather in an aqueousmedium at a pH of about 2.5 to 4.0 with a lower alkyl vinyl ether-maleicanhydride copolymer in which at least about 5 and no more than 15 of theanhydride groups have been converted to the salt-half amide with amember of the group consisting of ammonia and lower aliphatic primaryand secondary amines.

8. Hides, skins and leather treated by the process of claim 1.

9. A process comprising treating hides, skins and leather with a loweralkyl vinyl ether-maleic anhydride copolymer in which at least about 5and no more than 15 of the anhydride groups have been converted to thesalt-half amide with a member of the group consisting of ammonia andlower aliphatic primary and secondary amines and then dyeing the treatedhides, skins and leather.

10. The process of claim 1, in which the vinyl ether is vinyl methylether.

11. The process of claim 9 in which the vinyl ether is vinyl ethylether.

12. The products of the process of claim 9.

References Cited in the file of this patent UNITED STATES PATENTS1,976,679 Fikentscher Oct. 9, 1934 2,047,398 Voss et al. July 14, 19362,156,069 Schlack Apr. 25, 1939 2,160,375 Voss et al. May 30, 19392,205,882 Graves June 25, 1940 2,205,883 Graves June 25, 1940 2,220,867Kirk Nov. 5, 1940 2,313,565 McDowell et al Mar. 9, 1943 2,456,177 CupreyDec. 14, 1948 2,469,428 Beachell May 10, 1949 2,469,437 Kirk May 10,1949 2,543,602 Rowland Feb. 27, 1951 2,577,041 Seymour Dec. 4, 19512,609,350 Spatt Sept. 2, 1952

1. A PROCESS COMPRISING TREATING HIDES, SKINS AND LEATHER WITH A LOWERALKYL VINYL ETHER-MALEIC ANHYDRIDE COPOLYMER IN WHICH AT LEAST ABOUT 5AND NO MORE THAN 15% OF THE ANHYDRIDE GROUPS HAVE BEEN CONVERTED TO THESALT-HALF AMIDE WITH A MEMBER OF THE GROUP CONSISTING OF AMMONIA ANDLOWER ALIPHATIC PRIMARY AND SECONDARY AMINES.